1. Field of the Invention
The present invention relates to an image forming apparatus which records an image on a recording member such as a recording sheet and, more particularly, to a recording member feeding device for use on the image forming apparatus.
2. Description of the Related Art
One type of the recording apparatuses of the kind described above is an apparatus known as a xe2x80x9cserial printerxe2x80x9d in which a carriage carrying a recording head is moved in the widthwise direction of the recording member, thereby enabling the recording head to record information on the surface of the recording member.
In the operation of the serial recording apparatus, feed of the recording member and the recording performed by the recording head on the carriage are repeatedly performed in an alternating fashion, thereby performing recording on a certain area of the recording member.
In recent years, there has been an increasing demand for faster and quieter recording operations and, to cope with that demand, various improvements have been proposed with regard to the feeding of the recording member. One such improvement employs a detector which measures the amount of feeding operation of a feeder and which produces a signal for controlling a driving device such as a motor, thereby performing faster and quieter recording operation.
Demands also exist for higher quality recorded images, requiring a higher definition or fineness of recording which is achieved by the use of recording heads having smaller pixel pitches, and also requiring higher precision of feeding of the recording member.
Thus, greater precision of feed control is required, in addition to faster and quieter recording.
The above-described solution, however, encounters the following problems.
In the above-described configuration, which employs a detector for measuring the amount of feeding operation of a feeder and for producing a signal for controlling a driving device such as a motor, the feeding precision for recording member feed is primarily determined by the precision of detection performed by the detector.
Therefore, approaches have been made towards achieving higher resolution of the detecting element used in the detector, as well as greater fineness of an object, e.g., slits, to be detected.
Greater fineness of the detection object requires a finer pitch of the detection objects such as slits, as well as higher precision of machining of the detection objects.
This inevitably leads to a rise in the production cost. When a disk encoder scale for measuring the amount of rotation is used as the detection object, a higher resolution can be obtained by increasing the size of the disk, even if the pitch of the slit remains unchanged. Unlimited increase in the disk size, however, is not possible due to size requirements for the image forming apparatus.
On the other hand, detectors having higher resolution, i.e., higher detecting performance, are generally expensive and raise the production costs.
Another approach to achieving higher precision of feed of the recording member is to improve the mechanical precision of the parts of the recording member feeding device and driving unit, in particular to minimize eccentricities of rotary parts which are incorporated in transmission systems which transmit rotation.
Approaches have been made toward minimizing the influence of eccentricity, particularly when the object to be detected is, for example, a disk encoder scale used for measurement of rotation amount.
Hitherto, the amount of feed of a recording member has been directly measured or measured indirectly through detection of amount of rotation of another member, for example, a feed roller.
For instance, direct detection systems have been proposed in which a detection object such as a roller is held in contact with a feeding member or with the recording member, and the amount of feed is determined in terms of the product of the amount of rotation of the roller and the circumferential length of the roller, thereby enhancing the feeding precision, as disclosed in, for example, Japanese Patent Laid-Open Nos. 7-186484 and 8-90862.
This configuration, however, requires a roller and associated parts, resulting in higher production costs and greater size of the apparatus.
The detection system relying upon detection of amount of rotation of a feed roller also has a problem in that an exact 1:1 correspondence between the amount of rotation of the feed roller and the amount of rotation of an encoder scale as the detection object cannot be achieved, unless the feeding of the recording member is performed at a considerably large pitch.
Accordingly, it is an object of the present invention to provide a recording member feeding device, as well as an image forming apparatus, which is improved to achieve a higher precision of feed of the recording member while performing faster and quieter recording operations without causing a rise in the production cost, thereby overcoming the above-described problems of the known art.
To this end, according to the present invention, there is provided a recording member feeding device, comprising: a feeding rotary unit for feeding a recording member; a rotary driving unit for driving the feeding rotary means; a driving power transmitting unit for transmitting the driving power from the rotary driving unit to the feeding rotary means; and detecting unit provided in the rotary driving unit or in the driving power transmitting unit, for measuring the amount of rotation caused by the rotary driving unit.
Preferably, the arrangement is such that the number of complete rotations detected by the detecting unit is an integral multiple of the number of feeding operations performed by the feeding rotary unit.
In one form of the present invention, the detecting unit includes a detection object coaxially fixed to a rotary member of one of the rotary driving unit and the driving power transmitting unit, and a rotation sensor for measuring the amount of rotation of the detection object; wherein the number of complete rotations of the rotary member to which the detection object is fixed is an integral multiple of the feeding operations performed by the feeding rotary unit.
The arrangement also may be such that the rotary driving unit and the feeding rotary unit have rotary members drivingly connected to the power transmitting unit, and wherein the power transmitting unit is a speed-reducing transmitting unit in which the amount of rotation of the rotary member of the rotary driving unit is greater than that of the rotary member of the feeding rotary unit.
The present invention in another aspect provides an image forming apparatus in which the above-described recording member feeding device is associated with an image recording device which records an image on the recording member fed by the recording member feeding device.
In accordance with the present invention, it is possible to achieve a higher feeding precision of the recording member to improve image quality, as well as faster and quieter recording operation, without being accompanied by a rise in the costs or an increase in the size of the apparatus, by virtue of the provision of the detecting unit in the driving means or the driving power transmitting means and which detects the amount of the drive.
The amount of rotation of the rotary member in the driving unit or in the driving power transmitting unit is greater than that of the rotary member in the feeding unit, thus enhancing the resolution of the detecting unit with regard to the amount of feed of the recording member, thus contributing to improvement in the feeding precision.
Further, any undesirable effects produced by offset or eccentricity of the detection object to be detected by the detecting unit is canceled and, at the same time, the resolution of the detecting unit is enhanced, if the arrangement is such that the number of rotations detected by the detecting unit is an integral multiple of the number of the feeding operation performed by the feeding unit.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.